Optimal modes of side-section flow in heat-pump-assisted extractive distillation systems for separating allyl alcohol–allyl acetate mixtures with butyl propionate

Objectives. To investigate the influence of side-section flow modes on the energy efficiency of a partially thermally coupled distillation sequence (PTCDS) with a vapor recompression heat pump for the extractive distillation of an allyl alcohol–allyl acetate mixture with n-butyl propionate and identify modes under which the combined use of a PTCDS and heat pump are the most efficient.
Methods. Mathematical modeling in the Aspen Plus V10 software package was used as the main research method. The local composition equation of the non-random two-liquid model was used as a model for describing the vapor–liquid equilibrium, while the Redlich–Kwong model was used to consider the non-ideal vapor phase. When modeling the conventional extractive distillation scheme and PTCDS, parametric optimization was carried out according to the criterion of the total energy costs in the column reboilers. For the economical evaluation, Aspen Process Economic Analyzer V10.1 tools were used.
Results. For extractive distillation of a mixture of allyl alcohol (30 wt %) and allyl acetate (70 wt %) with n-butyl propionate as an entrainer, the minimum energy consumption was achieved at the same side-section flow mode for the variants of a PTCDS with and without a heat pump. The reduction in energy costs relative to the conventional scheme was 20% for the sequence without a heat pump and 38% for that with a heat pump. An economic assessment was made of the best options in comparison with the conventional extractive distillation scheme. The PTCDS with a heat pump had an advantage over the sequence without a heat pump only for long periods of operation.
Conclusions. For the extractive distillation of an allyl alcohol–allyl acetate mixture, the optimal modes for the combined use of a PTCDS with a vapor recompression heat pump coincide with the optimal modes for a PTCDS without a heat pump.

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